Electric locomotive



A. MA RossMAN 2,157,928

ELECTRIC LOCOMOTIVE Filed Dec. 26, 1935 3 Sheets-Sheet l May 9', 1939.

May 9, 1939. A. M. RossMANA ELECTRIC LOCOMOTIVE Filed Dec. 26, 1935 3 Sheets-Sheet 2 vvv l May 9,

ELECTRIC Filed Dec. 26, 1935 A. M. ROSSMAN LOCOMOTIVE 3 Sheets-Sheet 3 Hlllil Z Tener/ref'F/-aer 0x m *Vizi/6.4

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mma Mus. ma j i 2,157,928

UNITED STATES -PATENToFFlcl-z amm morale Locono'rlvn man u. naman. Wmme, n1.

am December ze. 19:5, serial Nn. 56,146

-19 can. (ci. 11s-m) The present invention relata generally to electype induction motors, each motor having but one tric traction and more particularry to a new sysset of three secondary collector rings. tem of prowlsion for electric locomotives and The system ofspeed control has as its basis, a the like, which can be adapted to cpcrate'elilnovel system of controlling the speeds of-wound cientlyonalternating current energyof any eomrotor type induction motors by controlling the 5 mercial frequency. -frequency of the energy in the secondary wind- In the present state of the art, alternating curings of the motors, shown and described in my rent systems of railway tion are sub- U. S. Pat. No. 2,087,782, dated July 20, 1937. to ject to one or more of the following disadvanwhich reference is hereby specifically made. lo tages; The speed control system disclosed in the present l. Impracticability of using energy at theusunl disclosure, can be adapted to provide at least commercial frequencies of 60 or 50 cycles, and evenly spaced, economical running speeds, and therefore, requiring either frequency converter any desired number of intermediate accelerating substations or separate generating equipment. steps. It centers in two or more 3-unit motor 15 2. Lack of flexibility, providing only two to generator sets, which, because of their manner l5 four economical running speeds. of use, are so small that they can be 'placed side 3. High losses in resistors and hence low eiilby side on opposite sides of a locomotive cab and ciency still leave ample aisle space between them.

4. Excessive weight and cost of locomotives, The characteristics and method of use of the 5. Extremely complicated system of propulsion, traction motors and control are such that they 20 employing electrical machines of unusual and will permit the locomotive to deliver its maximum special ccnstmctign tractivev elort throughout its speed range, includ- The principal object of the present invention ing that portion of the range in which the tracis to provide an electric locomotive of practical tion motors pass thlugh the speed zone which y 2:, design, which can be operated from a single embraces their synchronous speed. 25

phase, cycle or 50 cycle trc11cy A small direct-current exciter is the only com- Another object relates to the provision nf an mutator type machine required; all other elecelectric locomotive capable of carrying a high tral machines are nduCtiOn Or Synchronous tractive effort at high speeds. type machines.

2u Another object is to provide an induction mo- The locomotive is inherently regenerative and 30 tcldrivcn lgcomotvchaving a Satisfactory numregenerative braking is available over the entire ber of economical operating speeds. Speed range- A further object relates to the provision of an Energy W between trolley wire and locomoelectric locomotive having traction motors and tive iS at all Speeds approximately DlOlJOltiOnal :2.: control equipment of well known and proven tu the product of speed times tractive eiIort. 35

types, adaptable tc any commercial frequency E will now describe the construction and methstill another object relates to minimizing the od of operation 0f an embodiment of the present cost and weight of equipment consistent with the invention in which reference will be had to the results obtained following drawings which are appended to and .-l-r Another object has to do with the provision of @wie a par? 0f this disclosure 4o a system of speed control for alternating cur- Figure 1 1S a dagrfm in Plan 0f the anfangerent motors which utilizes the range of the auxlfivhe man Pleces 0f equipment m the iliary control equipment several times in accelcrating the motors over their speed range.

Another object relates to a method for accelercuits in the locomotive mpg induction motors from Zero speed up to an? Figure 4 is a set of curves showing the distridesued Super'synchronous speed under fm1 bution of power during acceleration and regen- Figure 2 is a similar diagram but in elevation. Figure 3 is a wiring diagram of the main cir- 45 torque during accelefationerative deceleration. 5 Further Objects Will be made apparent t0 thOSe Figure 5 is a set of curves showing the speed- 50 Skilled in the art, by the present diSClOSlletractive eiort characteristics of the locomotive. The System 0f Propulsion disclosed herein Like reference numerals refer t'o like parts draws single phase energy which is converted to throughout the specicatlon and drawings. 3 phase energy on the locomotive for use in the In Figures l and 2, the locomotive is shown 5 traction motors, which are simply wound rotor equipped with four driving axles 2A, 2B, 2C, 2D, 56

on which are wheels 3, each of the axles being driven by a pair of twin motors 4, respectively. As this arrangement of motors is well known to those skilled in the art, as well as the method of gearing to the axles by pinions t,- l, meshing with a single gear t, coaxial to and connected with the axle 2, these details are, for the sake of simplicitymerely indicated by outline.

A pony or guiding truck il, iii is shown at each end respectively of the locomotive, which is supported on a tracli il.

On each end ci the roof of the locomotive cab l is a current collector i2', i3 respectively, adapted to coact with the trolley wire l l.

For each pair of twin motors is provided a control motor generator set MA, MB, MC, MD respectively. The size of the control sets i@ is such that two can be placed-on each side of the aisle it, each pair arranged in two tiers, one set above the other. l

Each control set iii, is in itself, an adjustable ratio frequency converter. It comprises three machines, one of which it is a machine of a type known to those skilled in the art, in which the frame member usually known as the stator on l ordinary machines, is rotatably mounted on bearings so that it, as Well as the rotor, is independently rotatable.

inasmuch as the construction of this type of machine has been described in my previously tioned trunnion is elongated to provide a mounting for the rotor member of the second machine 22 of the control set. The latter machine, the frame o1 which is stationary, therefore is eiectively coupled with, and is adapted to control the rotation of, the rotatable frame member 2i.

The other trunnion ill forms a support for a set of collector rings 23, which are connected to the armature winding disposed within the rotatable frame member.

The rotor member is mounted on a shaft 2d which is coaxial to the trunnions and extends through them to bearings at each end respectively. On rotor shaft are disposed collector rings 2l for conducting direct current excitation to the field windings of the machine i6 which, as will be seen later, is preferably of the synchronous type.

Coupled to the rotor shaft 24 is a third machine 28. It is now evident that one of the auxiliary machines 22 controls the speed and direction of one oi' the rotatable members 2l, while the other auxiliary machine 28 controls the other member.

Another piece of equipment in the locomotive is a phase converter set 29, consisting of a phase converter 3U, an auxiliary machine 3l, and a small direct current exciter 32. although the latter machine could be driven by a separate motor if so desired. Although the phase converter could be of the conventional type, well known to those skilled in the4 art, I prefer to employ the' novel phase converter disclosed in my copending U. S. application, Serial No. 15,173. led April 8, 1935, to which specic reference is hereby made.

The phase converter shown in Figures 1 and 2 is electrically of conventional type as will be explained later. Mechanically, however, it is unusual in that it is a machine of the rotatable frame type, similar to the synchronous machines I6 of the control M-G sets I4. The frame 33 is supported by a pair of hollow trunnions 3l, 35 which are carried in bearings 3B, 3l respectively. On one of the trunnions is mounted a set of four collectorrings 34', which are connected to the armature windings of the converter. As the machine illustrated is of the squirrel cage type, there are no excitation collector rings, although this machine could well be oi the synchronous type.

The rotor shaft il@ of the converter is disposed concentric to and within the hollow trunnions 34, 35, and is supported in hearings 39, d0, at each end. The rotor member of the auxiliary machine 3i is mounted on an elongation of this shaft 38 between the bearings 36, 3Q. Hence, the auxiliary machine, which is of the conventional stationary frame type, controls the speed of rotation of the rotor shaft. .A reduced diameter shaft extension il carries the armature of the exciter 32.

The purpose of the rotatable frame in this machine is to provide a means for obtaining increased capacity from a core of given dimensions over that obtainable with a conventional machine, in order to conserve space and weight. The increase in capacity is explained as follows:

lt is well-known in the art of electrical machine design that the higher the peripheral speed of the rotor of an electrical machine of given core dimensions the greater is the capacity of that machine. The practice is therefore generally ollowed in designing an electrical machine, to determine the rotor diameter by the maximum permissible speed of that member. This speed is limited by the amount of centrifugal force that it is practicable to counteract by bracing the windings and anchoring the pole pieces and other parts of the rotating member.

A more fundamental factor in determining the capacity of a machine than the absolute speed of therotor, is the actual relative velocity between the rotor member and the frame member, usually known as the stator. Hence, if the rotor member be operating at its maximum mrmissible peripheral velocity in one direction or" rotation, the relative velocity between the two members can be greatly increased, if the 'frame member be likewise rotated at its maximum permissible velocity but in the opposite direction, thereby resulting in a corresponding increase in the capacity of the machine.

Take, for example, a machine, the rotor oi' which is designed to operate at 720 R. P. M. If the frame of this machine be rotated at 480 R. P. M. in the opposite direction, the relative speed between the rotor and frame will he increased from 720 R. P. M. to 12% R.. P. M., resulting in an increase in capacity of 67%.

The function of the auxiliary machine 3| is to hold the rotor shaft 38 vat its normal speed in one direction, while the converter 30 is connected to the supply of alternating current in suitable 'phase rotation so that the frame member 33 runs in the opposite direction.

`As the phase converter normally operates without substantial external mechanical load, the frame member merely idles at a constant speed which is equal to the normal speed of the ,converter, as determined by the number of electrical poles and the frequency of the supply, minus the speed of the rotor member.

- Hence, the auxiliary machine SI need not be designed to balance or resist the torque of the 'converter 30,' but need develop only a torque suiiicient to overcome the friction and windage of the element to which it is coupled. The auxiliary machine is also preferably used as a starting motor to bring the rotor member up to normal speed. The other member 33 can then be accelerated by applying voltage to the converter windings, as explained in more detail in my above-mentioned application.

Although a phase converter of conventional design would suilice, it would require more space in the locomotive. By this novel type of converter, I am enabled to obtain an arrangement of equipment in the locomotive such as is shown in Figures l and 2,which uses the available space to good advantage. A

The M-G sets are arranged in two tiers, two of the sets |4A, IIC being disposed above the other two sets I4B, IID respectively, the pedestal bearings ISC, C at the end of the upper set' I4C being carried on a base block 41 which rests on'the pedestals ISD, 25D of the lower M-VG set HD. Likewise, the pedestal bearings 26C, 26C at the other end of the upper synchronous machine I 6C are supported on a base block 46 which rests on the pedestals 20D, 26D of the lower M-G set I4D. The stator frames of the two end machines 22C, 26C are also supported on the stator frames of the lower machines- 22D, 28D. By locating the converter 25 and one pair of control M-G sets MC, I4D along one side of the cab, the two M-G sets disposed one above the other, and the other pair of M-G sets I4A, I4B, one above the other along the other side of the locomotive, opposite to the converter, and the transformer 4I opposite the pair oi M-G sets I4C, I4D, a suitable aisle I5 is provided down the center of the locomotive', and the weight of the above-mentioned machines is concentrated above the driving atles.

Referring now to Figure 3, the primary winding 42 of the single phase transformer 4I is connected between the current collector I3, `which contacts the trolley Wire II and the ground connection to the frame of the locomotive in the usual manner. Single phase power is supplied to the trolley wire and rails from a power system as is known by those skilled in the art. The sec. ondary winding 43 is connected to two conductors 44A, 44B of a three phase bus by a pair of conductors 45, 46.

The phase converter 30 can be either a synchronous or induction type machine. a squirrel cage induction machine has the advantage of simplicity, the synchronous type offers the possibility of power factor correction. For a complete description of this machine, reference is made to an article entitled Single-Phase Loads from Polyphase Systems," by B. G. Lamme, Electrical Journal, June, 1915, page 261.

A short explanation of that machine will suilice here. The converter 30 is Wound with two windings 5I, 52, in 90-degree relation to each other. One of the windings 5I is connected across the single phase secondary winding 43 of the transformer, with a tap changer 53 or other suitable device for adjusting the voltage on the winding. The other winding 52 is connected to the third phase conductor 44C of the bus by a conductor 55 and to the mid-point of the transformer through an adjustable voltage tap changer 54. The adjustable tap connectors 53, 54 on the transformer permit voltage changes to be made Although under different loading conditions, tomaintain substantially balanced three-phase voltages.

The auxiliary machine 3i is connected to the bus 44 through a starting Acontroller 56 which contains suitable equipment for starting andao ceierating one of the rotatable members of the converter on single phase power f rom the transformer.. After the converter is brought up to its -normal operating speed, the auxiliary machine 3| holds the absolute speeds of the rotatable members at suitable values.

nach of the four M-G sets e MA, MB, uc, un,

comprises the adjustable frequency machine I6, which is of the synchronous type, a wound rotor type induction machine 28 coupled to the rotor shaft 24. and a multi-speed, squirrel cage inducclarity, it is to be understood that any of the usual methods of reconnecting a winding to obtain two speeds may be employed if so desired; furthermore, although three speeds are used as illustration in this embodiment, otherrnumbers of speeds may be used in other embodiments of this system of speed control.

Each of the three windings is connected by a st of leads 51, 58, 59 respectively and switches 60, 6I, 62,' respectively to an intermediate bus 63. This bus can be connected to the three phase bus 44 by a pair of reversing switches 64, 65, by means of which the phase rotation in any of the windings and hence the direction -of rotationof the induction machine 22A can be con- -irolled.

The corresponding induction machine 22B of the second M-G set HB is similarly indicated as a three winding, three speed machine by the three sets of leads 66, 61, 68, which are connected in multiple with the three windings of the first mentioned induction machine 22A. Hence, it is evident that the speedcontrol switches 60, 6I, 62, as well as the reversing switches 64, 65, control both multi-speed motors 22A, 22B, simultaneously.

Provision is made for supplying direct current to one of the windings of each of the multi-speed induction motors from a suitable source of direct current by means of a switch 69, through an adjustable rheostat 12, and leads 1B, connected to a d.c bus 1I. The d.c. bus is supplied from the exciter 32. As is known to those skilled in the art. direct current fiowing in the windings of an induction motor has the eifect of braking the motor and locking its rotor and stator together. The purpose of holding these ma'- chines stationary will be explained later.

The wound rotor induction machines 28A, 28B of the first two M-G sets I`4A, NB, likewise have their primary windings connected in multiple to a set of leads 13 which are connected in turn to the bus 45 by reversing switches 15, 16,

by means of which the direction of rotation of nected by a set of leads 8i and a pair of reversing switches 32, 83 to an independent secondary bus 84, to which bus the secondary windings ci the pair ofl twin wound rotor induction type traction motors l, 5 are connected in multiple. Hence, it is evident that each synchronous machine controls the frequency of the energy in the vsecondary windings of the respective pair of i tively connected by a pair ci reversing switches til, Qt respectively to the main bus dit for either direction of phase rotation. Another pair oi reversing switches 89', dit is provided for connecting the lvl-G set bus lid to the main bus M in i either direction of phase rotation.

The induction machines 22C, 22D oi the other two lvl-G- sets are connected in parallel to the bus fifi by means of leads iii, iii?, the respective speed control switches 9d, @5, @6, and a pair of reversing switches @il One of the windings ci each ci lthe induction machines 22C, 22D are connected in parallel. to the d.-c, bus lli, through a d.-c. switch an adjustable rheostat 'i2 and leads lil.

cuit decreases.

l rheostat iii@ and wires idd.

rhcostat, the voltage and power factor of the The wound rotor induction machines 223C, @8D of the second pair oi lvl-G sets are likewise connected in parallel to the bus dd' through leads icl? and a pair of reversing switches lili, M32. An adjustable rheostat THC, iiD is connected in series with the secondary7 winding of each motor respectively.

The field windings of each synchronous machine it are excited by direct current supplied from. the d.c. bus 'di through an adjustable lEsy means of this circuit, including the synchronous machine i@ and the secondary windings ci the traction mocan be controlled. Furthermore, strengthening the iield oi the synchronous machine increases the synchronizing torque he tween the latter yrnacinne and the traction noo tors and hence the maximum pull-out torque ci the traction motors.

It is well known that when the speed of an induction motor is controlled by control of the frequency of the energy in either its primary or its secondary winding by means oi a synchronous machine operated at adjustable speeds, the synchronizing torque which tends to hold the two machines in synchronism drops ofi as the frequency of the energy in the interconnecting cir- However, the synchronizing torque decreases very little as the frequency decreases from normal value to half that value, that is, not more than 1li-20%. It is in the lower half of the frequency range that the torque drops rapidly.

Therefore, in order to obtain a satisfactory torque on the synchronous machine tending to hold it in synchronlsm with the traction motors throughout the entire speed range of the motors, and hence derive the maximum benet from the traction motors and control machines, the novel method of speed control which is described herein stant.

has been devised so that the frequency of the energy in the circuit, comprising the synchronous machine I6, interconnecting leads 8l, and the secondary windingsof the traction motors, never falls below half normal frequency.

The complete range of speed control of the traction motors is divided into three parts. In the irst part of the range, the primary windings of the traction motors are connected to the power supply, the frequency of which is of course con- The frequency of the energy in the secondary windings of the traction motors is then adjustaioly decreased from full to half the frequency of the supply, thereby accelerating the motors to half their rated synchronous speeds.

Now in the second part of the speed range, the primary windings are disconnected from the power supply and short-circuited, while the secondary windings are reversed in phase rotation with respect to the synchronous machine.

Whereas in the first part of the speed range, the

flow ci power was out from the secondary windings, in the second part of the range, the direction of power flow is into the secondary windings. In other words, the secondary windings now actually operate as primary Windingsjthe heretofore primary windings being short-circuited. However, in order .to avoid confusion, throughout this explanation and in the claims whichiollow, Ii will always refer to the winding which is connected to the power supply during part of the speed range, as the primary winding, and that winding connected to the synchronous machine as the secondary winding.

in the second part or" the speed range, the frequency of the energy flowing into the secondary winding is adjustably increased from half the supply frequency to a value appreciably higher than the supply frequency.

For the third part of the speed range, the primary winding is again connected to the power supply while the secondary frequency is adjustably increased from a value equal to the maximum value attained in the second part ci the range minus the power supply frequency, to any suitable maximum frequency. In the third part oi the speed range therefore, the traction motors are running above synchronism at supersynchronous speeds, and power `flows into the primary windings from the line, and into the secondary windings from the synchronous machines.

each change in connections of the machines necessitates a momentary interruption in torque, it is preferable to change connections on but a part or the motors at a time, during which change the remainder of the motors maintain the tractive eiort of the locomotive, or at least a corresponding percentage of its value before the switching occurs. To carry out this requirement,

the switching changes in the present embodiment are eiected on half the M-G sets at a time, as indicated by the parallel connection of the two wound rotor induction machines 28A, 28B, of the iirst two M-G sets, to the single pair of reversing switches 15, 1 6, and similarly the simultaneous control of the other two wound rotor induction machines 28C, 28D, by means of the other pair of reversing switches IIII, |02.

Likewise, the multi-speed induction machines are controlled in two groups, one group comprising the machines 22A, 22B of the iirst two M-G sets HA, MB, controlled in parallel by a common set of speed changing switches 60, 6I, 62 and reversing switches 64, 65. The other two multispeed machines 22C, 22D are also controlled in multiple by a common set of switches 9|, 8i, 96, 91, Sl'.,

The system herein described is not coniined to the number oi M-G sets and traction motors shown, although it may now be evident that there are certain requirements which must be met. There must be at least two M-G sets in order to hold tractive eiort on the locomotive during switching changes. At least, there must be two multi-speed induction motors so that one of them can be in connection at all times.

Another requirement is that any traction mo tors which are paralleled on both primary and secondary sides should also have a positive mechanical tie between them as well. That is to say, traction motor which are connected to different driving axles, which axles are not geared together or'connected by side rods or the like, should not have both their primary windings and their secondary windings connected respectively, in parallel. The reason for this is that when wound rotor induction motors are connected in parallel on both primary and secondary sides, they operate in synchronism with each other as is weii known to those skilled in the art. Hence, if motors so connected electrically, are coupled to different driving axles, any diil'erence in diameter of the driving wheels on those axles will tend to cause a difference in speed between the motors, but as the motors must all run in synchronism, some of the driving wheels must slip on the raiis and some of the traction motors will run as generators, their torque subtracting from the pulling power of the locomotive.

As each pair of twin motors IA, A, etc. is

geared to one axle, there is no tendency for them to run at different speeds and so they may be connected in parallel to the same M-G set. As four such driving axles are shown and there are nc .mechanical ties between them, the system requires four M-G sets. Four small M-G sets, however, are deemed to be preferable to two larger sets plus side rods or other mechanical tie between axles.

With this arrangement any slight differences between the speeds of the axles is reected back to the synchronous machine IB, which run at slightly different relative speeds between rotor and frame members. This difference can easily be compensated for by slight adjustments in the amount of resistance 11 in each of the secondary circuits of the wound rotor machines 28 of the M-G sets.

I will now explain in detail the operation of the novel system of speed control.

With the locomotive at standstill but in readiness to start, three phase power must oi course l be available at the bus M, hence the phase con-- is equal to the frequency ot the power supply.

Therefore, in order to connect the synchronous machine Ii to the secondary windings of the trac tion motors, the frequency of its generated voltage should also be equal'to the supply frequency.

Assuming the supply frequency to be 60 cycles, if the synchronous machine I6 has 6 poles, the

relative speed between rotor member-and framen ation they operate as induction generators.

member at the poire. of starring shouidbe 1200 R. P. M.

For this illustration, let the wound rotor induction machine 28 have 6 poles and the multi- 'speed induction machine 22 have three polegroupings of 12, 18 and 36 poles respectively.

By closingjthe proper switches and IBI and adjusting the rheostats 11, the wound rotor induction machines bring the rotor members of the several synchronous machines 16 up to approximately 1200 R. P. M. and the synchronous machines may be connected to the secondary windings of the traction motors by closing the proper switches 83,' after which the field excitation of the synchronous machines can be adjusted to suitable values by means of the eld rheostats |03. Now let the multi-speed induction motors be brought up to their lowest speed of approximately 200 R. P. M. by rst inserting a high resistance in the secondary control rheostats 1l, or preferably, opening these secondary circuits entirely, assuming the rheostats to have an open position, or innite resistance, and closing the proper speed selecting switches B0, 96 and closing the switch 54, 9S to select the proper direction of rotation, in the same direction as that of the motor members.

As the induction machines 22 accelerate to their lowest speed of 200 R. P. M., the wound rotor machines 28 are brought up to 1400 R. P. M., as the synchronous machines i6 are fixed at a relative speed of 1200 R. P. M. by the 60 cycle energy iiowing into their armature windings rom the secondary windings of the traction motions 4, 5, at which point the locomotive is ready to start.

Now by adjusting the rheostats 11, gradually y decreasing their resistance, the wound rotor machines 2B are brought from 1400 R. P. M. down to approximately 1200 R. P. M. during which oper- As the multi-"peed machines 22 are iixed at approximately 200 R. P. M., at the end of this operation the relative speed between the rotor and frame members of the synchronous machines I6 has been reduced to 1200v minus 200 or 1000 R. P. M., with a corresponding decrease in frequency in the interconnecting circuit 8i to 50 cycles. By this means the traction motors have been accelerated to one-sixth of their 60 cycle synchronous speed, or, assuming the traction motors each to have 12 poles, they are now operating at 100 R. P. M.

Power is now iiowing from the primary bus 85 at sixty cycles into the primary windings of the traction motors through the leads 81, one-sixth of which is used to run the traction motors, while the other five-sixths (neglecting losses) ows at 50 cycles from the secondary windings, through the leads Si, into the armature windings of the synchronous machines li. 'Ihe latter machines therefore operate as motors at a relative speed of 1000 R.. P. M., the rotor members driving the 1 wound rotor induction machines 28 as generators at 1200 R. P. M. while the multi-speed induction machines 22, operating as motors, drive the frame members at 200 R. P. M.; thereby supplying the diierence in speed between the 1200 R. P. M. of the wound rotor induction machines and the relative speed of 1000 R. P. M. between the me bers of the synchronous machines li.

The locomotive is now running at its rst economical running speed, which in this case is oneiifteenth, or 6.7%, of itsv maximum speed. It is an economical speed as no power is wasted in resistors afer therresistance in the rheostats I1 vthrough the traction motors and back to the bus *f by Way of M-GV sets.

Now to accelerate further, there must be some switching of speed connections, half the motors at a time. First the rheostat 11A, 11B are set in the open position and the multi-speed machines are connected on their 18-pole (400 R. P. M.) windings by opening the lowest speed switch 60 and closing the next switch 8|. As these machines rapidly accelerate to 400 R. P. M., the wound rotor machines 28A, 28B are brought up to 1000+400 R. P. M. or 1400 R. P. M. once more. Sufficient resistance is then inserted into the rheostats 11A, TIB to cause therst group of traction motors 4A, 5A, 4B, 5B to assume load while the switching operation is being carried out on the second group of motors 4C, 5C, 4D, 5D, which have maintained torque on their driving axles during the above described switching operation on the rst group of motors.

The second group of machines is switched in a manner similar to the above described operation. First the rheostats 11C, i'lD are set in theopen position, the multi-speed machines 22C, 22D are then connected on their lil-pole (400 P. M.) windings by opening the low speed switch 96 and closing the intermediate speed switch With all multi-speed induction machinesv 22 running at approximately 400 R. P. M. and all Wound rotor machines 28 running at approximately 1400 R. P. M., the locomotive is again accelerated to the next economical running speed of 13.3% of the maximum speed by gradually cutting out the resistance in the several rheostats 'l1 simultaneously, thereby decelerating the Wound rotor induction machines 28 down to approximate 1200 R. P. M. The relative speed between the two members of each of the synchronous machines I6 is thus reduced to 800 R.. P. M. so that the frequency of the energy in the secondary windings of the traction motors has been reduced to 40 cycles.

The third economical operating speed of the locomotive is attained by the method described above for accelerating from the first to the second speed. On the third speed connection, the multispeed induction machines 22 are connected on their highest speed connection by opening the intermediate speed switches 6l, 95 and closing the high speed switch 62, 94, and therefore operate at substantially 600 R. P. M. As the wound rotor induction machines 28 operate at 1200 R. P. M.

in the same direction, the relative speed between o rotor and frame members ofeach of the synchronous machines i6 is 600 R. P. M., which corresponds to 30 cycles in the interconnecting circuit. This frequency, which is half the value of that of the power supply, is the minimum to which it is desirable to extend the control because, as heretofore stated, the synchronous tie between the synchronous machine I5 and the traction motors begins to decrease in its effect rapidly as the frequency in the interconnecting circuit is further decreased, and the undesirable result of a decrease in this synchronizing torque xis a corresponding decrease in the maximum rateof acceleration of the locomotive.

At this point, therefore, a transition in connections of the rst half of the motors is made. 'I'he transition has as its object the change-over from estacas control of the frequency of the energy wing from the secondary Winding ofA each traction motor while energy is supplied from the bus to the primary winding, to control of the frequency of the energy supplied to one of the windings with the other winding short-circuited. 'I'he transition could have been made when the frequency of the energy owing from the secondary winding was at a greater value, say 40 cycles, by shortcircuiting the primary winding and then re-adjusting the relative speed between the rotating members of the synchronous machine to give 20 cycles, at which frequency the power could have been supplied to the secondary winding. Or, on the other hand, the transition could be delayed until the motors had accelerated to a higher speed when the frequency of the energy flowing from the secondary windings had been reduced to 20 cycles, whereupon after transition the frequency of the power supplied by the synchronous machine would be necessarily 40 cycles. In any case, after the transition the frequency of the energy supplied by the synchronous machine must be equal to the frequency of the power sup- -is required. The transition is made by opening the primary switches 86A, 86B, thereby disconnecting the primary windings of the traction motors 5A, 5A, iB, 5B from the power supply. At the same time, the secondary windings are disconnectedl from the synchronous machines by opening the'secondary switches 83A, 83B. The short-circuiting switches 88A, 88B, and Valso the other secondary switches 82A, 82B for reversed phase rotation are now closed, after which the traction motors operate at 30 cycles on the secondary windings on power which now flows from the synchronous machines I5, which now operate as synchronous generators. The wound rotor induction machines 28 now operate as motors instead of generators, while the multi-speed induction machines change from motoring to generating operation.

Now while the first half of the motors hold the tractive effort of the locomotive, the second half of the motors are put through a similar transition. The traction motors are disconnected by opening the primary and secondary switches 86C,

y06D, 83C, 83D respectively, and then the shortmotors from 30 cycles to 40 cycles.

As in previous steps, the secondary rheostats 'il of the first half of the equipment are set in the position 'of maximum resistance, which is preferably innte resistance with the rheostats in the open position. The multi-speed induction machines 22 are then switched to their intermediate speed of 400 R. P. M. by opening the high speed switch 62 and closing the intermediate speed switch 6|. As the machines decelerate from approximately 600 R. P. M. to 'approximately 400 R. P. M., the wound rotor induction machines 28 are decelerated fromapproximately 1200 R. P. M. to about 1000 R. P. M., as the synchronous machines I6 maintain their 30 cycle 75 relative speed of 600 R.. P. M. Finally, sufficient resistance is inserted in the rheostats 11A, 11B to cause the first half ofthe traction motors 4A, 5A, IB, 5B to assume the load,'and the reconnection can then be made on the second half of the motors 4C, 5C, 4D, 5D in a similar manner.

After the transition is compi'te, the resistance in all rheostats 11 is gradually 'cut out, thereby accelerating the wound rotor induction machines 28 from 1000 R. P. M. t0 1200 R. P. M. (minus the slip), which increases the frequency ci the energy supplied to the traction motors .from 30 cycles to 40 cycles, thereby accelerating them to 400 R. P. M. or 26.7% of the maximum speed.

Although for purposes of analysis, I have explained the transition and reconnection for the fourth step ci the speed range, as taking place in two separate or independent operations, in 'practice these two operations can be combined by reconnecting the multi-speed induction machines 22 at the same time that the primary and secondary reconnection of the traction motors is being made. During the reconnection the rheostats 11 should be set in the open position so that the wound roter induction` machines 28 will not exert torqueyresisting the change in speed of the multi-speed machines 22. After the latter machines have reached their new speed, the rheostats are adjusted to hold the torque o! the iirst haii' of the nic-tors while the second haii are put through a combined transition and reconnection, after which all rheostats are then adjusted to out out the resistance to accelerate the locomotive to the fourth operating speed.

A detailed explanation of the method of accelerating to the nfth speed of 33.3% of maximum is not necessary as it is similar to the others heretofore explained. In this step the speed of the multi-speed induction machines 22 is reduced to 200 R. P. M., and when the wound rotor induction machines have been accelerated,vby means of the rheostats 11, to 1200 R. P. M., the frequency oi the energy generated .by the synchronous machine I6 becomes 50 cycles.

To attain the sixth step, means are necessary for bringing the multi-speed machines 22 to rest 'and holding them stationary or substantially stationary, I prefer to accomplish this result by energizing at least one of the windings of these machines with direct current, by closingthe d.c. switches 69, 99 after opening the a.c. speed selecting switches. This method of braking an induction motor is known to those skilled in the art and needs no further explanation here than to say that the braking torque can be adjusted by adiusting the intensity of the direct current by means of the rheostats 12, 12'. Under direct current excitation the braking torque reaches a maximum value at a very low speed, approximately 2 or 3% of the normal rated speed. Hence, the machines 22 will thus be held nearly stationary, and the current required to do so is in the order of the value of full load alternating current in normal running operation, therefore forced ventilation of these machines is desirable.

With energy at 60 cycles supplied to the secondary windings of the traction motors, the primary windings `being short-circuited, the motors will run at substantially 600 R. P. M. (less slip), which is 40% of the maximum speed under this system oi control.

The seventh step oi control involves increasing the last mentioned frequency from 60 cycles to '10 cycles. In this switching operation, the d.c. switch 89 is opened and with the rheostats 11A, 11B open, the multi-speed induction motors are connected to their low speed windings but in the opposite direction of rotation to that heretofore taken. This is accomplished by opening the forward switch 64 and closing the reverse switch S5 and the low speed switch G0, then, by adjusting the rheostats 11A, 11B this group of traction motors 4A, 5A, 4B, 5B can be made to assume the load while a similar switching operation on the second 'group is accomplished, whereupon the multi-speed motors 22C, 22D are connected on their low speed windings but in the reverse direction through the reverse switch 01 and the low speed switch 96. By simultaneously but gradually cutting out all rheostats 11, the seventh running speed of 46.7% is attained.

On this running speed, the synchronous machines i6 supply 10 cycle power to the traction motors, at which frequency they operate at '100 R. P. M. (on the basis oi 12-pole motors).

On this step, the multi-speed machines .22 having been reversed in direction of rotation, they' now operate as motors instead of as generators. Hence', both induction machines 22, 2B now expend power upon the synchronous machine iB, which converts the mechanical power input to electrical power output at 70 cycles, and the rotor and frame of the synchronous machine gow run in relatively opposite directions of rota- It is now to benoted that the traction motors have passed beyond their synchronous speed with respect to the frequency of the power supply; therefore their primary windings could now be reconnected to the supply bus and with power at YAY cycles supplied to their'secondary windings they would then operate at super-synchronous speed. However, as has been stated hereinbefore, in order to obtain a synchronizing torque which approximates maximum normal value, the frequency in the interconnecting circuit between the synchronous machines I6 and traction motors I, 5 should be about half the frequency of the power supply.

Hence, it is preferable to continue the acceleration by further increasing the frequency of the power supplied to the traction motors to 90 cycles or thereabouts beforevmaking the transition. It is not believed that a detailed analysis is necessary of the next two steps wherein the frequency is raised rst to 80 cycles and then to 90 cycles as the method of switching is similar to that as heretofore given. Suffice it to say that the multi-speed motorsare first connected on their intermediate speed windings to obtain a speed of 400 R. P. M. on the frame of the synchronous machine, which, added to the 1200 R. P. M. of the motor, gives a relative speed between members of 1600 R. P. M., resulting in a generated frequency of 80 cycles. On the ninth step the multispeed machines are brought up, to their maximum speed of 600 R. P. M. resulting in a relative speed of 1800 R. P. M.. between rotor and frame which corresponds to 90 cycles on the assumption of a 6-pole synchronous machine.

Although it is not, of course, essential to carry the acceleration to any further extent, it is benecial to so do, as the increased speed land hence greater power output can be obtained with no extra expense in capacity of the traction motors or machines in the M-G sets. The reason for this is that as the torque has been assumed to Abe constant throughout the speed range," the current in the windings is constant throughout the range, and increased output of the traction motors is obtained by virtue of merely the increase in the speed of rotation. All that is necessary in extra design considerations is to adapt the construction of the traction motors to the higher maximum speed, which, in the example given herein, is 1500 R. P. M.

'I'he transition of the traction motors from operation at 90 cycles with one winding shortcircuited, to the same speed of rotation but operating with energy of the frequency of the supply system on the primary windings, it made by disconnecting the first half of the traction motors 4A, 5A, BB, 5B from the synchronous machines ISA, HGB by opening the secondary switches 82A, 82B, and also from the shortcircuit connection by opening the short-circuiting switches 88A, 88B. IThe frequency of the synchronous machine is then changed from 90 cycles to 30 cycles by reversing the wound rotor induction machines 28A., 28B by opening the rheostats 171A, 11B and also the primary switch l5, then closing the switch I6 for reverse phase rotation and cutting out the resistance in the secondary circuits by means of the rheostats 17A, THB. Thus, by plugging the wound movtor machines, they quickly deceierate.. reverse,

and accelerate to 1200 R. P. M. in the reverse direction, carrying with them the rotors of the respective synchronous machines. After this reversal, the relative speed between rotor and frame members becomes 600 minus 1200 R. P. M. or -600 R. P. M., which corresponds to cycles but in reverse phase rotation. In order to maintain the phase rotation in the same direction as before, 'the other switches 83A, 83B are now used toconnect thesynchronous machines to the traction motors, the direction of power flow being unchanged.

The primary windings of the traction motors are connectedto the primary bus 05 by closing the switches 86A, 86B.

However, the transition last explained would result in merely a change in circuits but no change in speed of the locomotive, a second switching change being necessary to connect for the next running speed. it is therefore preferable to combine these switching operations, as was done in connection with the previous transition.

Hence, during the reversal of the wound rotor machines 28A, 28B, the multi-speed machines 22A, 22B can be reconnected to their intermediate speed windings by opening the high speed switch 62' and closing the intermediate speed switch 0 l.' The multi-speed machines then decelerate the frame members of the synchronous machines to 400 R. P. M. while the wound rotor machines reverse and accelerate the rotor members in the same direction as that of the frame members. After the traction motors are reconnected by closing the switches 83, 86, the frequency in the secondary circuits is established at approximately 30 cycles, whereby determining the relative speed between the members of the synchronous machines at approximately 600 R. P. M. As the multi-speed machines are now connected for 400 R. P. M., the speed of the wound rotor machines Q8 must then be4 about 1000 R. P. M. By reducing the resistance in the rheostats 71A, 11B, the first group of traction motors' 4A, 5A, 4B, 5B will then assume load and hence hold the tractive effort of the loco-` motive while a similar transition is made on the second group of machines.

After the second half of the transition is accomplished, its Wound rotor machines 28C, 28D are likewise running at approximately 1000 R. P. M. in reverse direction, switch I 02 being closed, with resistance in their rotor circuits, the multi-speed machines 22C, 22D are running at 400 R. P. M. connected by the intermediate speed switch 95, and the traction motors 4C, 4D, 5C, 5D are connected to the synchronous machines ISC, ISD by switches 83C, 83D, and to the primary bus by switches 86C, 86D.

Now the-locomotive can be accelerated to its tenth operating speed by adjustably cutting resistance out of all of .the rheostats 11 simultaneously, thereby bringing the wound rotor machines 28 from 1000 to 1200 R. P. M. approximately, the frequency of the synchronous machine increasing from 30 to 40 cycles.`

rl'hus the traction motors are now operating at a supersynchronous speed of 66.6% higher than synchronous speed, or in the case of iZ-.pole machines, 1000 R. P. M. Power from the bus is supplied to the primary windings of the traction motors at 60 cycles and power converted by the frequency converter M-G sets it from 60 to 40 cycles, flows into their secondary windings. In the M-G sets themselves, power flows from the bus 64' to the wound rotor machines 28 to drive the synchronous machines i6 as generators and also the multi-speed machines 2 2 'as generators, returning power to the bus 't6'.

The remainder of the speed range consisting of the eleventh to the fteenth steps, is practically repetition of the fth to the ninth steps respectively, inasmuch as the switching changes effect an increase in frequency of the energy owing from the synchronous machine tothe traction motors from 40 to 90 cycles. The speed of the multi-speed machines is successively 200 R. P. M.; 0 R. P. M. (locked rotor); 200 R. P. M. in the opposite direction or that direction of rotation in which they operated originally in steps 1 to 5; then 400 R. P. M.; and lastly, 600 R. P. M. At each reconnection the speed of the wound rotor machines drops to 1000 R. P. M. which at each operating speed, is increased to approximately i200 R.. P.- M.

At the maximum speed of the locomotive, which is the fifteenth economical operating speed, the multi-speed induction machines 22 drive the frame members 2l of the synchronous machines i6 at 600 R. P. M. in one direction of rotation and the wound rotor induction machines 28 drive the rotor members at 1200 R. P. M. in the opposite direction of rotation, effecting a relative speed of 1800 R. P. M. between the two members. As the synchronous machines have 6 poles, this speed results in a generated frequency of 90 cycles, at which frequency, power is supplied to the secondary windings of the traction motors. With power at 60 cycles being supplied to the primary windings the traction motors therefore run atl speed of the locomotive and at each reconnection prior to acceleration from one sped to the next higher operating speed. The frequency of the energy iiowing in the primary windings and in the secondary windings of the traction motors is also shown for each condition.

15 -speed locomotive-motoring Locomotive Speeds o! machines of frequency speeds converter MG sets (R. P. M.) Frequency Wound Multx-speed 4 P machine and zlgreld Cycles Cycles Point er' frame of F prisecondcent rotor of relanve synch svnch. speed muy any mach mach.

U 0 0 +1200 1200 60 60 +200 +1400 1200 60 00 l 6.7 +200 +1200 1000 60 50 +400 +1400 1000 00 50 2 13.3 +400 +1200 800 60 40 +600 +1400 800 60 40 3 20 +600 +1200 600 60 30' +400 +1000 600 0 30 4 7 +400 +1200 y 800 0 40 li-m0 +1000 800 0 40 5 33.3 +200 +1200 i000 0 50 Y 0 +1000 1000 0 50 G 40 0 +1200. 1200 0 -00 200 +1000 1200 o so 7 46.7 m0 +1200 1400 0 70 -400 +1000 1400 0 70 8 53.3 -400 +1200 1600 0 80 -600 +1000 1600 0 80 9 60 -600 +1200 1800 0 90 -400 1000 ano 6o 3o l0 66. 7 -400 -1200 800 60 40 200 -1000 800 00 40 1I 73.3 -200 -1200 1000 60 50 0 -1000 1000 60 50 l2 80 0 1200 1200 60 60 +200 -1000 1200 60 60 13 86.7 +210 -1200 1400 60 70 +400 -1000 1400 00 70 14 93. 3 +400 -1200 1600 60 80 +600 -1000 1600 60 80 l5 100 +600 1200 1800 60 90 Itis to be understood that other speed combinations are to be contemplated for various operating conditions. For example, if a two-speed single winding induction machine having speeds of 600 and 300 R. P. M. be substituted for the 600, 400,200 R. P. M. machine, there will be .available evenly spaced economical running speeds Yinstead of 15. Furthermore, by providing the various machines with suitable numbers of poles, the system can be adapted for other frequencies, such as 50 cycles or 25 cycles.

When operating at any of the economical running speeds, the characteristics of the system are such that the speed of the locomotive is substantially constant, independent of load, and substan- Y tially independent of'whether the locomotive is motoring or regenerating. When an up-grade is encountered, the speed of the locomotive decreases only to the extent of the increase in slip of the induction type machines in the system, while if the locomotive encounters a down-grade, the locomotive speeds up only to the extent that the slips of the induction type machines change from one side of synchronismvto the other.

Furthermore, the control system can be used to decelerate, as well as to accelerate the locomotive. The method of control is similar to acceleration. In the embodiment described, assume the locomotive to be operating at its maximum on the fteenth step. To decelerate, the rheostats'TIA, '11B are set in the open position on the rst half of the machines, the multi-speed machines are then switched from high to intermediate speed by opening their high speed switch 62 and closing the intermediate speed switch 6l. As the multispeedl machines decelerate from 600 R. P. M. to 400 R. P. M., the wound rotor machines 28A, 28B accelerate to approximately 1400 R. P. M. as the relative speed between rotor and frame remains substantially 1800 R. P. M. Enough resistance is then inserted into the secondary windings bythe rheostats 11A, 11B, so that the iirst group oi' traction motors exert a torque which holds thetorque of the locomotive to prevent'itfrom accelerating if running on a downgrade, whilethe other group of motors is reconnected. Then, as all rheostats 11 are cut out simultaneously but gradually, the speed of the wound rotor machines 28 is decreased from 1400 to 1200 R. P. M. at which Vspeed the frequency in the synchronous machine thel traction motors which are operating as induction generators. Then one group of motors is disconnected, the frequency of the energy generated by the synchronous machines is adjusted to a value substantially fty per cent higher than the frequency of the power system, and the primary windings of the traction motors are-shortcircuited. The motors then regenerate power at 90 cycles, in this example, and hold the braking effort while the other group of motors is reconnecte'd. The frequency of the generated energy is then adjustably decreased to half the frequency of the power system or cycles. Again, one group of motors is disconnected, theirA primary windings connected to the power supply system and their secondary windings reconnected to the synchronous machine in reversed phase rotation, the frequency of the synchronous machine being adjusted, generally speaking, to a value equal to the frequency of the supply system minus the fre- Vquency to which the energy fiowing from the secondary windings, during the previous decelerating operation, was decreased. In the present example, however, the connection between the secondary windings of thetraction motors and the synchronous Amachines need only bereversed by means of the reversing switches 82, 83.

On the last decelerating operation, power is regenerated by the traction motors and returned to the system from the primary windings but energy must now be supplied to the secondary windings from the synchronous machines I6, operating now as generators, the frequency of the last-mentioned energy, being adjustably increased from 30 cycles to 60 cycles or power system frequency, at which frequency the traction motors zero, the multi-speed machines 22 are energized with direct current by closing the switch 69, 99, thereby holding the frame member 2| of the synchronous machine 16 substantially stationary during this last step.

usc

.i5-speed locomotive-Wowowo@ Locomotive S 'd ci machines of frequency 4 speeds verr M-G sets (nem.) Frequency Wound Multi-speed n I, machine and crho Cycles Cycles Point er' frame of f In prlsecondcent synch. rotori rea t117e mary any mh h.' ipe -1200 1800 60 90 5 ce" sa 1a a s 4 93.3 +400 1 +r is se e is 86.7 lo 6 l400 800 00 40 9 60 -000 -1200 600 60 30 -400 +1400 1800 0 90 8 53.3 -400 +1200 1600 0 80 -l +1400 1600 0 80 7 46.7 m0 -l-lm 1400 0 70 0 +1400 1400 0 70 6 40 0 +1200 1200 0 00 +m0 +1400 1200 0 00 5 33.3 +200 +1200 1000 l0 60 +400 +1400 1000 0 50 4 1? +400 +1200 800' 0 40 +600 +1400 800 0 40 3-;.---- m +000 +1200 600 0 30 +400 +1000 600 60 30 2 13.3 +400 +1200 800 60 40 +200 +1000 800 60 40 1 6.7 +200 +1200 1000 60 50 0 +1000 1000 60 50 0 0 0 +1200 1200 60 60 To start the locomotive in the opposite or reverse direction of motion, the phase rotation on the primary bus 85 and the M-G set bus M are reversed by opening the bus switches 90, 90. and closing the switches 89, 89'. The only immediate eiect of this switching operation is the reversal of the wound rotor machines 28 as the multispeed machines 22 are stationary when the locomotive is stationary. It is desirable to insert some resistance into the rheostats Il to cushion the surge of currentinto these motors when they are thus reversed.

Control during operation in the reverse direction from this point on is`no different than by the method described hereinbefore.

Inasmuch as the speed of the locomotive is always substantially constant for each connection, if the power supply to the locomotive fails momentarily during operation it is not necessary to bring the locomotive to rest in order to reconnect the machines for operation, but the locomotive may coast along until the power is restored, the secondary reversing switches 82, 83 being held open. 'I'hen when the power is restored, it is necessary to merely determine the actual speed of thelocornotive by speedometer or other suitable means, reconnect the machines of the M-G sets with resistance inserted in the rheostats 11 for the speed connection which corresponds nearest to the actual speed, and close the proper secondary switches. Any discrepancy in speed will cause the wound rotor machines 28 to change speed, the rheostats il acting to cushion the surge of current due to the discrepancy in speed. The rheostats can then be adjusted to cut lout the resistance, thereby accelerating or decelerating to the said nearest operating speed.

Referring now to Figure 4, the power output o1' the locomotive during acceleration is indicated by. the straight lines'AB, corresponding to a conescasas ostats 'il in accelerating from each point to the next, is indicated by the series of small triangles DE, FGI-i, etc. Hence, the energy input to the locomotive y(neglecting machine losses) is equal to the output plus the resistor loss and is therefore indicated by the outline of the series of steps DEFGH, etc. from A to B. The curve is based on the assumption that when the locomotive delivers maximum tractive eiort, the machines temporarily are subjected to double load.

The maximum value of power dissipated in resistors at maximum tractive effort is only oneflfteenth o1' the power input at maximum speed and maximum tractive effort.

During deceleration by regeneration, assuming the same constant torque on the motors, the energy generated bythe traction motors is indicated by the straight line BJ. This power is returned to the system with the exception of machine losses (neglected) and the losses in resistors, in-

I dicated by the triangles KLM, MNO, etc.y Therefore, the power regenerated back to the bus is converter 30 must have the capacity to convertv it to three phase power. In practice, however, many if not most locomotive applications do not require that the maximum tractive eiort be maintained up to full speed, and very few locomotives are capable of so maintaining their tractive effort.

In such an application therefore it is possible to reduce the capacity and therefore the weight and cost of the transformer and phase converter of a locomotive of the type disclosed herein, to a capacity which allows full tractive eiort up to a predetermined locomotive speed with a constant horsepower characteristic above that speed.

Figure 5 illustrates this principle. 'I'he line PQ is the constant tractive eifort based on 100% overload on the traction motors, transformer, and phase' converter during acceleration, maintained up to full speed, while the constant tractive effort based on normal loading isvshown by the line RS, or of the maximum tractive eiort. If the transformer and phase converter be reduced to one-half the size necessary to maintain the tractive effort curve PQ, the maximum tractive eiort will be that indicated by the-line PV up to half speed and then along the constant horsepower curve VS. The tractive effort curve corresponding to normal load on the transformer and phase converter in this case is shown by the curve PTU.

I do not intend my invention to be limited to the details shown and described herein, except as they are recited as essential in the appended claims.

I claim:

1. Apparatus for controlling the speed of an electric locomotive having a plurality of driving axles, comprising in combination an A. C. motor connected to each of said axles, a source of alternating current, a plurality of adjustable ratio frequency converters adapted for electrical connection to said motors and switching means co-operative with said converters, for controlling the frequency of the energy supplied to said motors, said switching means being adapted for successively switching less than all of said converters at' a time, thereby maintaining torque on at least one of said axles during the switching operations.

2. In a vehicle having a plurality of driving Y axles, a set of induction motors connected to each of said axles, a source of alternating current, an adjustable ratio frequency converter individual to each of said sets of motors for converting power flowing between said source at constant frequency and said motors at adjustable frequency, and switching means co-operative with said converters, for controlling the ratio of frequency conversion, said switching means being adapted for successively switching approximately one-half of the converters at a time, thereby maintaining torque on approximately one-half of thedriving axles during the switching operation.

3. In an electric locomotive having a plurality of driving axles, a wound rotor type induction motor connected to each of said driving axles, each of said motors having a primary winding and a secondary winding, a source of alternating current, meansfor connecting the primary winding of each of said motors .to said source,l an adjustable ratio frequency converter for each of said motors, said converters being connected between said source and said secondary windings respectively, and switching means co-operative with said converters for controlling the frequency of the energy interchanged between said source and said secondary windings, said switching means being adapted for successively switching part of said converters at a time, while the remaining converters maintain torque on at least part of said axles during the switching operations.

4. 'Ihe method of accelerating a wound rotor type induction machine from zero speed, through its normal synchronous speed to 'a predetermined supersynchronous speed, comprising supplying energy from a constant frequency source to the primary winding of said machine and adjustably reducing the frequency of the energy lflowing from the secondary winding yto a predetermined value, then short circuiting one of said windings and adjustably increasing the frequency of the energy input to the other of said windings to a value higher than said constant frequency, then again supplying energy from said source to the primary winding and supplying energy at adjustable frequency to the secondary winding, and adjusting the latter frequency to obtain the predetermined supersynchronous speed.

5. The method of accelerating a wound rotor type induction machine from zero speed to a predetermined supersynchronous speed. comprising supplying alternating current from a constant frequency source to the primary winding of said machine and adjustably reducing the frequency of the energy flowing from the secondary winding to a predetermined minimum value, therebyaccelerating said machine to a corresponding subsynchronous speed, then with the primary winding short-circuited, supplying alternating current to the secondary winding at a frequency which is -substantially equal to that of said constant frequency source minus said minimum value, then.

increasing the frequency in said' secondary winding to a predetermined maximum value which is substantially higher than that of said source, Ithen again supplying energy' from said source at constant frequency to the primary winding and supplying alternating current to the secondary winding at a" frequency which is substantially equal to said maximum value minus the frequency of said source, and lastly, increasing the frequency in the secondary winding to attain said predetermined supersynchronous speed.

6. The method of accelerating a wound rotor type induction machine from zero speed to a predetermined supersynchronous speed, comprising supplying energy from a constant frequency source to the primary winding of said machine and adjustably reducing the frequency of the energy flowing from the secondary winding to substantially half the frequency of said source, thereby accelerating said machine to substantially half of its synchronous speed, then with one of said windings short-circuited, supplying alternating current to the other winding at substantially half the frequency of saidy source, then increasing the frequency of the last-mentioned energy to a value which is substantially fifty per cent higher than that of said source, then again supplying energy from said source at constant frequency to said primary winding and supplying energy to said` secondary winding at a frequency equal to substantially half that of said source, and finally increasing the frequency of the energy in said secondary winding to accelerate said machine to said predetermined supersynchronous speed.

7. The method of decelerating a wound rotor type induction machine connected to a power system, from a supersynchronous speed down to standstill, comprising adjustably reducing the frequency of the energy flowing from the secondary winding of the machine to substantially half the frequency of the power system,.the power output of the primary winding of said machine being returned to said system,`then disconnecting and short-circuiting the primary winding and adjustably reducing the frequency of the energy flowing from the secondary winding from a va'lue substantially fifty per cent higher than that of said power system to a value substantially onehalf of the frequency of the power system, then reconnecting the primary winding to the power system, supplying energy to the secondary winding at half the frequency of the power system and finally increasing the frequency of the last-mentioned energy to a value equal to that of the power system.

8. 'I'he method of accelerating a plurality of wound rotor type induction machine connected to a common load, to a predetermined supersynchronous speed, without interrupting the torque exerted against said load, comprising supplying energy from a constant frequency source to the primary windings of said machines and adjustably reducing the frequency of the energy owing from the secondarywindings to half the frequency of said source, then disconnecting a num` ber less than all of the machines, short-circuiting their primary windings respectively, and supplying energy to their secondary windings at half the frequency of said source, then repeating the three last-mentioned steps successively on the remainder of the machines, then adjustably increasing the frequency to a valuev substantially higher than that of said source, then again disconnecting a number less than all of the machines, supplying energy to the secondary windings thereof at a frequency equal to said higher value of frequency minus that of said source, and supplying energy to the primary windings from said source, then repeating the three last-mentioned steps successively on the remainder of the machines, and finally adjusting the frequency of the energy supplied to the secondary windings to adjust the speed of said machines to said predetermined supe'rsynchronous speed.

9. The method of decelerating a plurality of Wound rotor type induction machines mechanically connected to a common rolling load and electrically connected to a power system, from a supersynchronous speed down to standstill without interrupting the braking torque exerted against the load, comprising adjustably decreasing the frequency of the energy owing from the secondary windings of the machines to substantially half the frequency of the power system, the power output of the primary windings being returned to said system, then disconnecting and short circuiting the primary windings of a number less than all of the machines, receiving power from theI secondary windings thereof at a frequency substantially fifty per cent higher than that of the system, then disconnecting and shortcircuiting the primary windings of the remainder of the machines, then adjustably reducing the frequency of the power flowing from the secondary windings of all the machines to a value substantially half that of the power system, then reconnecting the primary windings of a number less than all of the machines to the power system and supplying energy to the secondary windings thereof at substantially half the frequency of the power system, then repeating the two last-mentioned steps on the remainder of the machines, and finally increasing the frequency of the 'energy input to the secondary windings to a value equal to that of the power system.

10. The method of starting and accelerating an induction machine having a primary winding and a secondary winding, by means of an auxiliary machine connected to said secondary winding by an electric circuit, said auxiliary machine being adapted for adjusting the frequency of the energy flowing in said circuit, wherein the maximum torque which can be exerted by said induction machine varies over a greater range, with variations in the frequency of the energy in said circuit below a predetermined value of frequency, than for equal variations in frequency above said predetermined value, said method comprising supplying electric energy at constant frequency to said primary winding, adjustably decreasing the frequency of the energy in asaid circuit from the frequency of said supply to said predetermined value, then disconnecting said primary winding from the constant frequency source of energy, adjusting the frequency of the energy in said electric circuit to the proper value and reversing the phase rotation of the energy in said secondary winding, short-circuiting said primary winding, and finally increasing the frequency of the energy in said circuit to the desired value.

1l. The method of starting and accelerating aninduction machine having a primary winding,

and a secondary winding, by means of an auxiliary machine connected to said secondary winding by an electric circuit, said auxiliary machine being adapted for adjusting the frequency of the energy flowing in said circuit, wherein the maximum torque which can be exerted by said in` aisance ing energy at said rated frequency to said primary windings, adjustably decreasing the frequency of the energy to half of said rated value, then disconnecting the primary winding from the source vof supply, reversing the phase rotation of the voltage impressed on said secondary winding and short-circuiting said primary winding, and nally increasing the frequency of the energy in said secondary winding to any suitable value.

12. A system of adjustable speed control, comprising in combination, a supply of alternating current, a main induction machine having a primary winding and a secondary winding, means connected to one of said windings for interchanging energy between the last-said Winding at adjustable frequency and said supply at constant frequency, control means foradjusting the frequency of the energy in the last-said winding, switching means for selectively connecting the other of said windings to said supply during operation within a part of the speed range of said machine, and means for selectively short-circuiting the last-said winding during -operation within another part of said speed and a secondary winding, means comprising a synchronous machine electrically connected to said secondary winding for adjusting the frequency of the energy flowing in said secondary winding, and switching means for selectively either connecting said primary winding to said I'supply or short-circuiting thc last said winding.

14. An adjustable speed drive, comprising in combination, a supply of alternating current, a

load shaft, a main induction machine coupled thereto, said machine having a primary winding and a secondary winding, a synchronous machine having a winding, means for connecting the last said winding in series with said secondary winding, means coupled to said synchronous machine, for adjusting the frequency of the energy flowing in said series connected windings over a range which extends both above and below the frequency of said supply, and switching means for selectively either connecting said primary windiug to said supply or short-circuiting the last said winding.

l5. An adjustable speed drive, .comprising in combination, a supply of alternating current, a load shaft, a main induction machine coupled thereto, said machine having a. primary winding and a secondary winding, a synchronous machine having an armature winding, means for connecting said armature winding in series with said secondary winding, means coupled to said synchronous machine, for adjusting the speed of said machine and hence the frequency of the energy flowing in said series connected windings over a range which extends from substantially half the frequency of said supply to a maximum value appreciably higher than the frequency of said supply, switching means for selectively connecting said primary winding to said supply for starting said main machine and accelerating it tohalf synchronous speed, by adjustably reducing the frequency in said series connected windings from a valuev equal to that of said supply, to half said value, and switching means for selectively shortcircuiting said primary winding and for reversing the relative phase rotations in said series connected windings, -whereby said main machine can be further accelerated to a speed appreciably higher than its rated synchronous speed by increasing the frequency in said series connected windings to said maximum value, and whereby said main machine can be operated over a further range of supersynchronous speeds when said primary winding is again connected to said supply.

16, An adjustable speed drive, comprising in combination, a supply of alternating current, a load shaft, a main induction machine coupled theretoi said machine having a primary Winding and a secondary winding, a synchronous machine having an armature Winding, said synchronous machine having a rotor member and a frame member, each of said members being rotatably mounted on hearings, means for selectively operating one of said members at a plurality of substantially constant speeds, means for adjustably controlling the speed of the other of said members over a range equal to at least the diillerence between said constant speeds, for adjusting the frequency of the energy flowing in said armature winding, switching means for connecting said armature winding in series with said secondary Winding, and switching means for selectively either connecting said primary winding to said supply or short-circuiting the last said winding.'

17. An adjustable speed drive, comprising in combination, a supply of alternating current at constant frequency, a main induction machine having a primary winding and a secondary winding, switching. means for optionally connecting said primary winding to said supply or short circuiting said primary winding, and means for sup piying alternating current at adjustable ire'- quency to said secondary winding selectively in either direction of phase rotation.

18. An adjustable speed drive, comprising in combination. a supply of alternating current at constant frequency, a main induction machine having a primary winding and a secondary winding, switching means for optionally connecting said primary winding to said supply or short circuiting said primary winding, means providing a source of alternating current at frequencies adjustable over a range which extends both above and below the frequency Vof said supply, and

switching means for connecting said adjustable frequency source to said secondary winding se lectively in either direction of phase rotation.

19. An adjustable speed drive, comprising in combination, a main induction machine having a primary winding and a secondary winding, an adjustable frequency machine having an arma= ture winding, switching means for connecting said armature winding in series with said second ary winding in either direction of phase rotation, said adjustable frequency machine having a rotor member and a frame member. each of said members being rotatably mounted on bearings, a mul1 ti-speed squirrel cage machine coupled to one of said members, a wound rotor induction machine coupled tothe other of said members, switching control means for controlling the speeds of each of said last named induction machines, a source of alternating current. and switching means for selectively either connecting said primary Wind ing to said source or short crcuiting said winding,

ALLEN M2 ROS. 

